This is a grant application to continue our studies of antibodies to the simple antigenic determinants phosphocholine (PC), group A streptococcal carbohydrate (GAC) and alpha (1 yields 3) dextran. Our goal in these studies is to provide evidence of how antibody diversity is generated. In particular, in the present proposal we address questions about how diverse antibodies really are and whether evolutionary relationships are preserved among antibodies with similar specificity. In addition, we will examine questions concerning combinatorial diversity generated by heavy-light chain pairing and whether VH genes pair randomly with all CH genes. Finally, we will probe the relationship of VH region expression and L chain expression.